Method and device for monitoring the effectiveness of vehicle braking systems

ABSTRACT

The present invention relates to a method and to a system for monitoring the effectiveness of rail vehicle braking systems and, in response to certain criteria, initiating one or more of a safety braking and a switching-off of a brake-force-limiting or brake-force-reducing device of the braking system when a defined desired slip is not reached.

[0001] The present invention relates to a method and to a device for monitoring the effectiveness of braking systems of vehicles, particularly rail vehicles.

[0002] Braking control systems have the purpose of converting a braking request defined by the driver into a vehicle deceleration. The monitoring of whether the desired vehicle deceleration results from the braking request is normally left to the driver. In the case of rail vehicles, the train engineer, in particular, has the task of recognizing danger situations, such as a faulty response of the braking system or a failure of the braking system and of initiating a safety braking. For avoiding accidents, it is mainly required that disturbances be recognized in time and an emergency braking takes place immediately.

[0003] It is an object of the invention to provide a method and a system respectively for monitoring the effectiveness of vehicle braking systems.

[0004] This object is achieved by means of claims 1 and 10. Advantageous developments and further developments of the invention are indicated in the subclaims.

[0005] The invention is based on the idea of comparing a driver's braking request with the occurring vehicle reaction and of detecting possibly occurring disturbances by a sequential examination of several response criteria and of initiating a emergency or safety braking.

[0006] When a braking request of the braking system is not converted into the requested vehicle deceleration, the monitoring device automatically initiates an emergency braking. In this case, existing operating or environmental conditions of the vehicle, such as the slope of the route, the coefficient of adhesion between the wheel and the rail, etc. are taken into account, so that the vehicle deceleration requested by the driver or the vehicle decelerations maximally possible as a result of the physical marginal conditions are achieved.

[0007] The “automatic braking intervention” can take place by way of “signal paths” which, in the case of conventional rail vehicles are to be activated by the driver, as well as by additional intervention possibilities, as, for example, by switching off braking-force-limiting or braking-force-reducing systems. In other words, the invention suggests that, instead of the emergency impact button which is normally provided in rail vehicles and is to be operated by the driver, an “intelligent impact button” be provided which is automatically triggered in an emergency and, if necessary, the anti-skid protection system be switched off.

[0008] The invention therefore permits a fastest possible initiation of safety brakings in the event of recognizable disturbances in the braking system. This relieves the driver and significantly increases safety. It is also advantageous that faulty partial systems of the braking system, for example, the anti-skid protection system, can be switched off automatically. The actually available braking force can therefore be optimally utilized; that is, it can be prevented that the driver erroneously decelerates the vehicle by means of a lower braking force level than the physically transmissible braking force level.

[0009] In the following, the invention will be explained in detail by means of an embodiment in connection with the drawing.

[0010] The single FIGURE 1 shows the process steps to be carried out according to the invention which are carried out in practice by means of an electronic control device or by a microcomputer.

[0011] In this process, the following quantities are used as input quantities:

[0012] v: speed of the vehicle above ground

[0013] -b_(desired): the desired deceleration of the vehicle corresponding to the driver's braking request

[0014] v_(i): wheel speeds

[0015] F_(i): braking forces at wheels or axles.

[0016] When a disturbance in the braking system is detected, the following output signals can be generated:

[0017] A signal for the automatic initiation of a safety braking and/or

[0018] a signal for switching off the anti-skid protection system.

[0019] In Step 1, it is determined whether a driver's braking request is present, Step 1 being constantly repeated when no braking request is present. If a braking request is present, the vehicle speed is determined in Step 2, specifically independently of the operation of the braking system. In this case, the determination of the vehicle speed v takes place by a separate measuring device which is provided specifically for monitoring the effectiveness of the braking system. This can take place, for example, by a radar speed measuring system or by the separate sensing of the speed of an unbraked axle. The vehicle speed can also be determined in a known manner by analyzing rotational wheel speed signals. Here, an analyzing algorithm is to be used which operates independently of the algorithm for determining a reference speed for normal service brakings by the brake control system.

[0020] In Step 3, the actual vehicle deceleration -b_(actual) is computed in a known manner from the vehicle speed v. In Step 4, a desired vehicle deceleration -b_(desired) is determined from the braking request defined by the driver.

[0021] In Step 5, the desired deceleration and the actual deceleration are compared with one another; and, in Step 6, it is decided whether the deviation between the desired value and the actual value can be tolerated. In the comparison between the desired deceleration and the actual deceleration, environmental parameters, such as the slope of the driving route, are taken into account. In this case, it is checked, for example, whether the following relationship has been met:

|-b _(actual)|≧-b _(desired)|−g*tan_(α),

[0022] g being the location factor of the acceleration due to gravity; and α being the angle of slope or inclination of the driving route. If the deviation between the actual vehicle deceleration and the desired vehicle deceleration is considered to be tolerable, a return takes place to Step 1. Otherwise, braking forces F_(actual,i) at individual wheels or axles are determined in Step 7. During the braking force monitoring, it is checked whether the braking forces at the individual wheels or axles correspond to the values which are required for reaching the requested vehicle deceleration -b_(desired). The braking forces F_(desired) necessary for reaching the requested vehicle deceleration are determined in Step 8 as a function of the requested vehicle deceleration b_(desired) determined in Step 4.

[0023] In Step 9, it is checked whether the actual braking forces are greater than the desired braking forces, that is, whether the following applies:

F _(actual,i) ≧F(-b _(desired))_(desired,i).

[0024] The braking forces at the individual wheels or axles can be determined by measuring, for example, by measuring the brake pressure, or can be estimated on the basis of the brake cylinder pressures or other known quantities of the braking system. If the braking force is sufficient, a return takes place to Step 1. However, if the braking force is too low, a slip monitoring is carried out. For this purpose, in Step 10, first the wheel slip S_(actual,i) at individual wheels or axles is determined according to the following formula: ${\begin{matrix} v_{i} \\ v \end{matrix}s_{{actual},i}} = {{1\quad--} - .}$

[0025] If necessary, when determining the slip, peculiarities of the basic braking system are taken into account. Thus, for example, in the case of an anti-skid control per bogie, it may be sufficient for an axle in the bogie to reach a defined minimal slip.

[0026] In Step 11, the slip signals s_(i) are compared with the minimal slip s_(min); that is, it is checked whether $1 - {\begin{matrix} v_{i} \\ -> \\ v \end{matrix}{s_{\min}.}}$

[0027] For each wheel or each axle, the checking is linked with a time criterion. In Step 12, the results for the individual wheels or axles are combined to a sum statement, that is, to a summation slip signal. In Step 13, the summation slip signal is compared with a defined desired slip. If the desired slip has been reached, a return takes place in Step 14 to Step 1. If, however, a deviation exists which cannot be tolerated, an automatic safety braking is initiated in Step 15, and/or the anti-skid protection system is completely or partly switched off in Step 16. 

We claim:
 1. A Method for monitoring the effectiveness of braking systems of rail vehicles, the steps comprising: determining whether a driver's brake request is present; determining vehicle speed; determining actual deceleration of the vehicle from the vehicle speed; comparing the actual deceleration with a desired deceleration; determining actual braking forces at one or both of individual wheels and axles; comparing the actual braking forces with desired braking forces which are required for reaching the desired deceleration when a deviation between the desired deceleration and the actual deceleration exceeds a defined tolerance value; determining actual slip values at one or more of individual wheels and axles comparing the actual slip values with a defined minimal slip when the actual braking forces are lower than the desired braking forces; summing the actual slip values of one or more of individual wheels and axles to a summation slip signal; initiating one or more of a safety braking and switching-off of a braking-force-limiting or brake-force-reducing device of the braking system when a defined desired slip is not reached.
 2. The method according to claim 1, wherein the vehicle speed is determined by a separate measuring device which is independent of a speed measuring device provided for control or regulating of normal service brakings.
 3. The method according to claim 1, wherein the vehicle speed is determined by a radar measuring system.
 4. The method according to claim 1, wherein the vehicle speed is determined by measuring the speed of one or more of an unbraked wheel and an unbraked axle.
 5. The method according to claim 1, wherein during the comparison of the actual deceleration with the defined desired deceleration, the slope of the vehicle's driving route is taken into account.
 6. The method according to claim 1, wherein during the comparison of the actual wheel slip values with the minimal slip, a time criterion is taken into account.
 7. The method according to claim 1, wherein the switching off of one of a braking-force-limiting and brake-force reducing device includes one or more of completely and partially switching off of an anti-skid protection system of the vehicle.
 8. The method according to claim 1, further including measuring the actual braking forces.
 9. The method according to claim 1, estimating the actual braking forces based upon brake cylinder pressures.
 10. (Deleted)
 11. (New) A system for monitoring the effectiveness of braking systems of rail vehicles, comprising: at least one sensor for sensing a driver's braking request; at least one sensor for sensing the rail vehicle's speed; at least one sensor for determining actual braking forces at one of individual wheels and axes; and determining actual deceleration of the vehicle from the vehicle speed, comparing the actual deceleration with a desired deceleration requested by the driver, comparing the actual braking forces with desired braking forces required for achieving the desired deceleration when a deviation between the desired deceleration and the actual deceleration exceeds a defined tolerance level, determining actual slip values at one or more of individual wheels and axes from wheel speeds and the vehicle speed, comparing the actual slip values with a defined minimal slip when the actual braking forces are lower than desired braking forces, summing the actual slip values and generating a summation slip signal, and generating a signal for initiating one of a safety braking and a switching off of one of a braking-force-limiting and brake-force-reduction device of the braking system when the defined minimal slip is not reached. 